Steering System For Crane

ABSTRACT

A steering system ( 10 ) for a vehicle, such as a gantry crane ( 12 ). The gantry crane ( 12 ) generally includes a support structure ( 14 ) having a first front wheel ( 32 ) and a second opposing front wheel ( 36 ) connected proximate a front portion of the crane ( 12 ), and a first rear wheel ( 30 ) and a second opposing rear wheel ( 34 ) connected proximate a rear portion of the crane ( 12 ). A control system connected to the crane includes a user interface ( 111 ) electronically coupled to a command potentiometer ( 114 ) and a programmable controller responsive to the command potentiometer for controlling the angular position of each of the first front wheel ( 32 ), the second front wheel ( 36 ), the first rear wheel ( 30 ) and the second rear wheel ( 34 ) to effect a steering mode selected through the user interface ( 111 ).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of and claims the benefitof co-pending U.S. application Ser. No. 11/058,738, filed Feb. 15, 2005,which is incorporated by reference herein and made a part hereof.

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

None.

TECHNICAL FIELD

The invention relates to steering systems for cranes and, moreparticularly, to a four-wheel steering system for a gantry crane.

BACKGROUND OF THE INVENTION

Steering systems for industrial cranes such as gantry cranes are wellknown in the art. Gantry cranes are used for lifting and transportinglarge cargo containers to and from railroad cars, truck trailers andother locations as well as for lifting and transporting boats. Anoperator utilizes the steering system to navigate the gantry cranethrough rail yards, warehouses, boat yards or other locations. While thesteering systems according to the prior art provide a number ofadvantageous features, they nevertheless have certain limitations.

The present invention is provided to overcome certain of theselimitations and other drawbacks of the prior art, and to provideadvantages and aspects not provided by prior steering systems. A fulldiscussion of the features and advantages of the present invention isdeferred to the following detailed description, which proceeds withreference to the accompanying drawings.

SUMMARY OF THE INVENTION

The present invention provides a steering system for a crane. In onepreferred embodiment, the steering system is used on a gantry crane.

According to one aspect of the invention, a steering system for a craneis provided. The steering system comprises a first front wheel and asecond opposing front wheel connected proximate a front portion of thecrane, a first rear wheel and a second opposing rear wheel connectedproximate a rear portion of the crane; and a control system connected tothe crane. The control system includes a command potentiometer, a userinterface electronically coupled to the command potentiometer, and aprogrammable controller responsive to the command potentiometer forcontrolling the angular position of each of the first front wheel, thesecond front wheel, the first rear wheel and the second rear wheel toeffect a steering mode selected through the user interface.

The steering system is configured to implement a number of safetyfeatures. The crane includes an engine for driving the wheels connectedto the crane which is capable of operation at a variety of differentRPMs. In one embodiment, the control system includes a sensor coupled tothe engine and the controller for providing the controller with anoperating RPM of the engine. The controller is configured so that if theoperating RPM is lower than a predetermined amount, the controlleradjusts the rate of change of the angular position of each wheel. Thecontroller slows down the rate of turning of each wheel to coincide withthe sensed engine RPM.

The control system includes a first sensor for monitoring the angularposition of the first front wheel, a second sensor for monitoring theangular position of the second front wheel, a third sensor formonitoring the angular position of the first rear wheel, and a fourthsensor for monitoring the angular position of the second rear wheel. Thefirst, second, third and fourth sensors are coupled to the controllerwherein the controller monitors the angular positions of the wheels.According to another safety feature, when one of the wheels exceeds apredetermined distance between its sensed position and programmedposition (this can happen if a wheel is in a rut), the controller stopsangular movement of the remaining wheels until the out of position wheelis at its programmed position.

The controller is also programmed to slow down movement of the cranebefore effecting a carousel steering mode selected through the userinterface. To position the wheels of the crane into the proper steeringposition for the carousel mode as efficiently as possible, thecontroller is programmed to move the angular position of each wheel oneof clockwise and counter clockwise, to effect the smallest amount ofangular movement necessary.

The user interface can comprise a proportional device that provides adirection and a magnitude signal. For example, the proportional can be ajoystick.

According to another embodiment of the invention, a steering system forcontrolling the steering mode of a crane comprises a crane structurehaving a first front wheel proximate a front portion of a first side ofthe crane structure, a second front wheel proximate a front portion of asecond side of the crane structure, a first rear wheel proximate a rearportion of the first side, and a second rear wheel proximate a rearportion on the second side. A user interface for selecting a steeringmode is either mounted to the crane or coupled to the crane via a remotecontrol. A controller connected to the crane is communicatively coupledto the user interface. The controller is configured to monitor theposition of the first and second front wheels and the first and secondrear wheels, and to control movement of the first and second frontwheels and the first and second rear wheels in response to a selectedsteering mode. The controller further configured to monitor an operatingparameter of the crane, such as engine RPMs.

The controller is further programmed to disable an engine drive of thecrane prior to positioning the wheels in a selected steering mode, andto enable the engine drive after the wheels are in position to effectthe selected steering mode. In particular, this is done when selecting acarousel steering mode.

The controller senses the position of each wheel when implementing theselected steering mode and the rate each wheel is turning to the desiredfinal position. The controller will disable movement of all wheels upona determination that at least one wheel is not moving to a desiredposition at a desired rate. This may indicate the problem wheel is in arut or has some other malfunction requiring user intervention.

In one form, the user interface is mounted to the crane andcommunicatively coupled to the controller via a wire. Alternatively, theuser interface is mounted to a radio transmitter and is communicativelycoupled to the controller via radio frequency transmissions.

The steering system further comprises a command potentiometer coupled tothe user interface and the controller. The position of each wheel isresponsive to the command potentiometer.

The controller is further configured to monitor the drive engine RPMrate. The controller lowers a rate of turning each wheel to a desiredposition for the selected steering mode upon sensing a low RPM rate.

The steering system is configured to cause the first front wheel and thesecond rear wheel to rotate counterclockwise to move into position for aselected carousel steering mode, and to cause the second front wheel andthe first rear wheel to rotate clockwise to move into position for thecarousel steering mode. The system then reverses the drive direction ofthe second front wheel and the second rear wheel.

According to yet another embodiment of the invention, a steering systemfor controlling the steering mode of a large vehicle, such as a gantrycrane or other large vehicle is provided. The steering system comprisesa vehicle having a drive engine mechanically coupled to a plurality ofwheels positioned to effect movement of the vehicle, and a controllerconnected to the vehicle configured to implement a user selectedsteering command. The system further includes a plurality of firstsensors coupled to the controller. Each first sensor is further coupledto one of the plurality of wheels. A signal from each first sensor tothe controller provides an indication of the respective wheel position.Additionally, the system includes a user interface coupled to thecontroller for providing a user selected steering command, and aplurality of hydraulic motors coupled to the controller. Each motor isalso coupled to one of the plurality of wheels of the vehicle to rotatethe respective wheel upon receipt of a wheel position command signalfrom the controller.

The system also includes second sensor (or a plurality of secondsensors) coupled to the controller for sensing a parameter (or a numberof parameters) of the vehicle. This can enable the system to monitor theparameters and adjust the steering system as needed.

Other features and advantages of the invention will be apparent from thefollowing specification taken in conjunction with the followingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

To understand the present invention, it will now be described by way ofexample, with reference to the accompanying drawings in which:

FIG. 1 is a perspective view of a gantry crane with the wheelspositioned in a carousel steering mode according to one aspect of thepresent invention;

FIG. 2 is a perspective view of the gantry crane of FIG. 1 with thewheels positioned in a crab or traverse steering mode;

FIG. 3 is a perspective view of the gantry crane of FIG. 1 with thewheels positioned in a two wheel front steering mode;

FIG. 4 is a top plan view of a gantry crane in accordance with an aspectof the present invention illustrating positioning of the wheels in thecarousel steering mode;

FIG. 5 is a top plan view of the gantry crane of FIG. 4 illustratingpositioning of the wheels in the crab or traverse steering mode;

FIG. 6 is a top plan view of the gantry crane of FIG. 4 illustratingpositioning of the wheels in the two wheel front (and two wheel rear)steering mode(s);

FIG. 7 is a top plan view of the gantry crane of FIG. 4 illustratingpositioning of the wheels in a coordinated steering mode;

FIG. 8 is a graphical illustration of components for turning andmonitoring the position of the wheels of the gantry crane of the presentinvention;

FIG. 9 is a schematic diagram for a hydraulic circuit for controllingthe steering components of the gantry crane;

FIG. 10 is a portion of a schematic diagram of an electrical controlcircuit for the steering control system of a gantry crane in accordancewith an embodiment of the present invention;

FIG. 11 is another portion of the schematic diagram of FIG. 10;

FIG. 12 is a perspective view of the “steer right” and “steer left”controls for use with an embodiment of the steering control system; and,

FIG. 13 is a perspective view of controls for controlling selection ofthe steering mode of the steering control system.

DETAILED DESCRIPTION

While this invention is susceptible of embodiments in many differentforms, there is shown in the drawings and will herein be described indetail preferred embodiments of the invention with the understandingthat the present disclosure is to be considered as an exemplification ofthe principles of the invention and is not intended to limit the broadaspect of the invention to the embodiments illustrated.

FIG. 1 shows a steering system 10 operably connected to a vehicle, suchas gantry crane 12. However, it is understood that the steering system10 can be connected to other types of cranes. The general structure ofthe gantry crane 12 will first be described followed by a description ofthe steering system 10. It is understood the description of the gantrycrane 12 component is exemplary and could vary depending on the type ofcrane or gantry crane utilized.

The gantry crane 12 generally includes a gantry structure 14 having aright side support frame 16 and a left side support frame 18 (referenceto the “right” and “left” sides is from the perspective of one viewingthe gantry crane 12 as it appears in FIG. 1). The right side supportframe 16 and the left side support frame 18 are substantially identicalin significant respects.

Referring to FIG. 1, the right side support frame 16 includes a rightrear vertical leg 20, a right front vertical leg 22, a right upper sidebeam 24 and a right lower side beam 26. The upper side beam 24 and thelower side beam 26 span between and connect the right rear vertical leg20 and the right front vertical leg 22. An upper cross beam 28 extendsbetween and is connected to the right side support frame 16 and the leftside support frame 18. A right rear wheel 30 is located near a lower endof the right rear vertical leg 20 and a right front wheel 32 is locatednear a lower end of the right front vertical leg 22.

Also referring to FIG. 1, the left side support frame 18 also similarlyincludes a left rear vertical leg 20 a, a left front vertical leg 22 a,a left upper side beam 24 a and a left lower side beam 26 a. The upperside beam 24 a and the lower side beam 26 a span between and connect theright rear vertical leg 20 a and the right front vertical leg 22 a. Aleft rear wheel 34 is located near a lower end of the left rear verticalleg 20 a and a left front wheel 36 is located near a lower end of theleft front vertical leg 22 a.

The wheel base of the gantry crane 12 is the distance between the rearwheels 30, 34 and the front wheels 32, 36. The width of the gantry crane12 is the distance between the right side wheels 30, 32 and the leftside wheels 34, 36. The upper cross beam 28 connecting the right sidesupport 16 and the left side support frame 18 can be adjustable. Forexample, the upper cross beam can include a flanged joint or otherstructure to allow for adjusting the length of upper cross beam 28, andthus the width of the gantry crane 12.

It is understood that the four wheels 30, 32, 34, 36 allow for a mobilegantry structure 14. As explained in greater detail below, the steeringsystem 10 monitors and controls the position (i.e., angle) of the wheels30, 32, 34, 36 to control the direction of movement of the gantry crane12. An operator cab 38 is shown attached to the right side support frame16 at the right rear vertical leg 20 a. It is understood that theoperator cab 38 can take other forms and be positioned at differentlocations. The operator cab 38 could also be mounted for vertical and/orhorizontal movement between various locations.

As further shown in FIG. 1, the gantry crane 12 has a lifting assemblyoperably attached to the gantry structure 14. The lifting assemblyincludes a right front load block 42 and a right rear load block 44operably connected to the right side support frame 16. A left front loadblock 46 and a left rear load block 48 are similarly attached to theleft side support frame 18. Attached to and suspended from the four loadblocks 42, 44, 46, 48 are sling assemblies 39 used to lift objects suchas, for example, large boats or other loads. It is understood that thesling assemblies 39 could also be replaced by a spreader attachment thatis specifically designed to lift truck trailers or large cargocontainers. The load blocks 42, 44, 46, 48 operate collectively to raiseand lower the sling assemblies 39.

Each wheel 30, 32, 34, 36 has a hydraulic assembly 100 connectedthereto. The hydraulic assembly 100 is also operably connected to thesteering system 10. As graphically illustrated in FIG. 8, each hydraulicassembly 100 includes a hydraulic motor 102 with a pinion drive gear104. As explained in greater detail below, each hydraulic assembly 100receives control or turn signals from the steering system 10 andoperates accordingly to rotate the respective wheel to a desired (i.e.,programmed) position. Other systems can also be used for turning thewheels. For example, a hydraulic cylinder system with appropriatelinkages can be used in place of the hydraulic motor 102 and piniondrive gear 104. Such hydraulic cylinder systems used in steering systemsare known in the art.

The steering system 10 is uniquely configured and programmed to monitorand control the position of the wheels 30, 32, 34, 36 as well as variousoperating parameters of the gantry crane 12 for steering the crane. Inaddition to the wheels 30, 32, 34, 36, the steering system 10 generallyincludes the following components: a controller 110; hydrauliccomponents (including the hydraulic assembly 100) controlled by thecontroller 110 for turning the wheels 30, 32, 34, 36, a user or operatorinterface 111, and a motorized master control potentiometer 114. Thecontroller 110 is uniquely programmed to accommodate the varioussteering modes and safety functions described herein.

Preferably, the steering system 10 utilizes an IQAN based steeringcontrol system (which is manufactured by Parker). An IQAN system isparticularly applicable for electronically controlling and monitoringhydraulics in mobile machines, such as a mobile gantry crane.Additionally, the IQAN system can be configured to communicate withother systems or components in the gantry crane 12. The IQAN system canbe programmed by a user of the system via a high level graphical designtool.

The IQAN system can comprise one or more IQAN modules. Preferably, oneof the modules is a master module 116 having a display unit. The masterIQAN module 116 is responsible for implementing the programmed steeringmodes of the gantry crane 12. As illustrated in FIGS. 10 and 11, themaster module 116 is electronically connected to a first additional IQANmodule 118 (e.g., an IQAN-XT2), a second additional IQAN module 120(e.g., an IQAN-XP2), and a third additional IQAN module 122 (e.g., anIQAN XS) which assist in controlling the steering functions of the crane12 under the control of the master module 116. Collectively, the IQANmodules function as the controller 110. The program can be set to allowan operator to interface with the program through the controller 110.

Steering of the gantry crane 12 is controlled by a master command valueprovided by an operator of the gantry crane 12. The user or operatorinterface 111 for providing the master command can be in a variety offorms, such as switches, a paddle or a steering wheel. Moreover, themaster command can be implemented mechanically or through the software.One preferred operator interface is a proportional device that commandsa direction and a magnitude (i.e., the magnitude reflects the speed thatthe steering direction is changed) such as a joystick 112. Theproportional device controls as DC motor which is connected by a driveshaft to the motorized master control potentiometer 114. Operatormovement of the interface 111 activates the motorized master controlpotentiometer 114 to implement the desired steering functions. Theposition of each of the wheels 30, 32, 34, 36 is compared to the masterpotentiometer by the controller 110. The DC motor is adjustabledepending on the engine RPMs.

The operator interface 111 is preferably housed in the operator cab 38.The IQAN modules 116, 118, 120, 122 can also be housed in the operatorcab 38, or more preferably, in a separate cabinet 124 connected to thegantry crane frame 14. In the embodiment shown in FIG. 1, the cabinet124 is connected to the right lower side beam 26. The display unit canbe placed in the operator cab 38 via an electrical connection.

The IQAN controller 110 is also capable of interfacing with existingradio remote transmitter and receiver technology. Accordingly, thesteering system 10 can also be operated by a radio remote transmitter orother remote control device (not shown).

The program run by the controller 110 controls the steering modes of thesystem 10 in response to input from an operator through the userinterface 111. The various steering modes include: two wheel frontsteer; two wheel rear steer; four wheel carousel steer; four wheel crab(or traverse) steer, and four wheel coordinated steer. Other steeringmodes can also be programmed into the controller 110 as desired. Thedifferent steering modes can be selected from the machine control panel(i.e., the user interface 111) or from the radio remote transmitter.

Each wheel 30, 32, 34, 36 is controlled independently. Preferably, thecontroller 110 will attempt to rotate the angle of each wheel (about alongitudinal axis 150—see e.g., FIG. 4) at a rate so that all the wheelswill reach the desired position for a newly selected steering mode atthe same time.

One embodiment of the user interface 111, in the form of a control panelwith a plurality of control switches, is shown in FIG. 12. Primarycontrol of the steering is done through a “steer left,” or “steer right”command implemented by the operator through a steer left/steer rightcontrol switch 126 on the interface 111. In the absence of a steer rightor steer left command, the system will implement a “straight ahead”command as a default (assuming the crane is in one of the steering modesapplicable). The steer left/steer right control switch 126 may return toa neutral position after implementation of a steering command (this willalso occur with the use of a proportional device, like a joystick).However, the steering system is programmed to maintain the steeringdirection until the operator commands the steering back to “straightahead” or another direction. The “straight ahead” (or “home”) commandwill return the wheels 30, 32, 34, 36 of the gantry crane 12 to thestraight ahead or home positions at a predetermined or commanded rate.The actual straight ahead or home positions are programmed into thecontrol system and can be adjusted mechanically on the machine or viathe software. For purposes of this application, movement in thedirection from the operator cab 38 toward the upper cross beam 28 willbe referred to as the forward or “straight ahead” direction, withopposite movement being the back or rear direction. A control 128 isused to determine the direction of the crane.

As illustrated in FIG. 8, each wheel 30, 32, 34, 36 of the gantry crane12 is provided with a positional sensor, such as a rotary potentiometer130. The rotary potentiometer 130 transmits a signal corresponding tothe wheel angle (i.e., the wheel position) to the controller 110. Theangle of the wheel is measured with respect to the axis of the upper andlower side beams 24, 26 and 24 a, 26 a (depending on which side 16 or 18of the gantry crane 12 the wheel is connected). The controller 110compares the actual position of the wheel with the desired programmedposition for the steering mode selected. In this manner, the controller110 is able to continuously monitor the position of each wheel 30, 32,34, 36 and actively control the position by sending the appropriate turnsignals to the hydraulic assembly 100 associated with turning eachwheel. As discussed in more detail below, the controller 110 can turneach wheel either clockwise or counter clockwise, as necessary, to getthe wheel in position for a newly selected steering mode as quickly andefficiently as possible.

The actual movement of the steering wheels 30, 32, 34, 36 can be doneindependently. That is, no mechanical linkage to the other wheels isnecessary. The wheels can be steered with hydraulic cylinders, hydraulicmotors, or an electric actuator motor. A gear box may be used to matchthe steering device to the wheel. Preferably, the gantry crane 12 willuse Parker L90 electro-hydraulic proportional valves along withhydraulic motors to move the steering wheels.

Referring to the embodiments of the user interface 111 in FIGS. 12 and13, a first steering mode selector switch 132 and a second steering modeselector switch 134 are utilized to allow the user to select thesteering mode. The switches 132, 134 can be multi-positional toggleswitches as shown in the FIGs. The first steering mode selector switch132 allows the operator to select either the two-wheel front steering,or the two wheel rear steering modes.

If a four wheel mode is desired, the first steering mode selector switch132 is moved towards the arrow pointing to the second steering modeselector switch 134. In this position, selection of the steering mode isthen determined by the second steering mode selector switch 134. Thesecond steering mode selector switch 134 allows the user to select thefour wheel coordinated steering mode, the four wheel carousel steeringmode, or the four wheel crab or traverse steering mode. The electricalconnections of the switches 132, 134 are illustrated in FIG. 10.

The four wheel carousel steering mode is illustrated in FIGS. 1 and 4.In this mode, the controller 110 sends signals to the hydraulicassemblies 100 for each of the four wheels 30, 32, 34, 36 to positionthe wheels at an approximately ±43.67 degree angle from the “straightahead” position generally aligned with the side beams 24, 24 a, 26, 26a. This angle may vary depending on the size of the crane (i.e., thewheel base and width distances). Specifically, as shown in FIG. 4, thefront right wheel 32 is turned inward (i.e., counterclockwise) 43.67degrees, and the right rear wheel 30 is turned outward (i.e., clockwise)−43.67 degrees. Similarly, the left front wheel 36 is turned inward(i.e., clockwise) −43.67 degrees, and the left rear wheel 34 is turnedoutward (i.e., counterclockwise) 43.67 degrees.

The controller 110 turns each respective wheel either clockwise orcounterclockwise (about the longitudinal axis 150) to its desiredposition to minimize the amount of turning required. That is, if thewheels only turned in one direction, for example—counterclockwise, thefront left wheel 36 and the right rear wheel 30 would have to travel316.33 degrees from the straight ahead position to get into the propercarousel mode position (as discussed below, this was done in the pastbecause each wheel could only be rotated about its axle in onedirection). The steering control system 10 includes a pressurecompensated hydraulic pump that is connected to a right side steeringcontrol valve and a left side steering control valve. Each valve has twosections, one for controlling the front wheel and one for the rear wheelof the respective sides. The pump is preferably continuously pressurized(e.g., 3500 psi at idle), so the operator doesn't have to wait for thepressure to build up before the controller 110 can turn the wheels.Instead, the valves will open in the proper direction at the commandedrate upon selection of a steering mode. As illustrated in FIGS. 10 and11, the system includes a right side steering control valve control 140and a left side steering control valve control 142. Each control 140,142 can turn the respective wheels clockwise (“cw”) or counterclockwise(“ccw”) as desired.

Positioning of the wheels 30, 32, 34, 36 in the carousel mode causes thegantry crane 12 to spin about a central point 104. To accomplish this,the controller changes the direction of movement of the wheels (i.e.,about the rotational axis 152 of the wheel—see e.g., FIGS. 1-3) on oneof the sides 16, 18 of the crane 12. To travel counterclockwise aboutthe center point 105 of the crane 12 as viewed from above, the drivingdirection of the left side front and rear wheels 36, 34 is reversedwhile the right side front and rear wheels 32, 30 remain going forward.Conversely, to travel clockwise about the center point 105, thedirection of right side front and rear wheels 32, 30 is reversed, whilethe left side front and rear wheels 36, 34 remain going forward. Asillustrated in FIG. 11, the system controls a reverse drive solenoidvalve 146 to implement this feature of the carousel mode.

In operation, once the operator selects the carousel mode, thecontroller 110 disables the drive engine during transition to correctthe position. The wheels are then rotated to the desired positions, andthe drive direction of rotation is reversed for two of the wheels. Thecontroller then enables the drive engine.

FIG. 2 and FIG. 5 show the gantry crane 12 in the four wheel crab ortraverse steering mode. In this mode, the wheels 30, 32, 34, 36 arepositioned generally transverse to the forward (i.e., straight ahead)and backward directions of the crane 12 (i.e., approximately ±90degrees). This allows movement of the gantry crane 12 in the transversedirection (i.e., sideways—similar to movement of a crab). Moreover, thewheels 30, 32, 34, 36 can be adjusted (i.e., turning the wheels slightlyaway from 90 degrees, for example, by 10 degrees) to steer the gantrycrane 12 while in the transverse mode. This provides a component ofmovement in the forward or backward directions while moving the crane 12transversely.

As shown in FIG. 3 and FIG. 6, the front wheels 32, 34 are rotated toeffect steering of the gantry crane 12 in the two wheel front steeringmode, while the rear wheels 30, 34 are kept in a fixed “straight ahead”position (to move the crane forward—i.e., in the direction of the cab 38toward the cross-beam 28). Alternatively, these same wheels 32, 34 canbe used to effect steering of the gantry crane backwards in the twowheel rear steering mode. Conversely, it is possible to rotate the rearwheels 30, 34 to effect the two wheel rear steering mode in the forwarddirection or the two wheel front steering mode in the rear position. Inthis embodiment, the front wheels 32, 34 will be fixed in the “straightahead” position.

In the four wheel coordinated steering mode, the controller 110 canrotate (i.e., turn) each of the wheels 30, 32, 34, 36 to steer thegantry crane 12. This can be useful, for example, to provide a tighterturning radius for the crane 12.

The steering system 10 includes various safety features. One safetyfeature is invoked when a new steering mode is selected by the operator.In this instance, the prior mode running at the time of the newselection will not change until the control system determines it is safeto change steering modes. This helps prevent damage to the crane oritems attached to or carried by the crane, or an inadvertent change tothe steering mode. Determining whether it is safe to change modes candepend on a number of different factors, such as the present speed ordirection of the crane, as well as the current position of the wheels.For example, when changing to certain modes, the control system will notallow the new steering mode to actually change until the wheels allcross a point near the straight ahead direction. Similarly, the controlsystem will not allow a change to certain steering modes unless thecrane is stopped. Specifically, in the case of changing to the carouselsteering mode, the control system will not allow the new steering modeuntil the crane is stopped.

In another safety feature, if the controller 110 senses that one (ormore) of the wheel(s) 30, 32, 34, 36 cannot reach its desired (i.e.,commanded) position for any reason (for example, the wheel is movingslowly or stuck in a rut), the control system will limit the movement ofthe other wheels to limit the error between the desired wheel positionsand the actual wheel positions of all the wheels 30, 32, 34, 36. This isto limit the amount of stress on the frame of the gantry crane 12 if oneor more of the wheels does not go to its desired position. If the stuckwheel(s) becomes free to move (for example, the crane 12 is moved out ofthe rut), it will then seek its desired position. The maximum errorallowed between the desired position of the wheels and the actualposition of the stuck wheel(s) can by adjusted by the operator and/orimplemented in the steering program. For example, if the differencebetween the actual position and the programmed position exceeds athreshold (e.g., three degrees) for any wheel, the controller 110 stopsturning the other wheels to their programmed position until thesituation is corrected (e.g., by another steering command or removal ofan obstacle, such as by requiring the operator to drive the crane 12forwards or backwards until the wheel is clear). In this manner, thewheel that moved the least (i.e., the stuck wheel) will determine thedesired position of the other steering wheels.

The control system will retain the current steering mode setting whenthe power is turned off and will not change the steering mode when poweris restored unless the proper conditions are met to allow change to anewly selected mode.

To implement steering the gantry crane 12, as well as certain of thesafety features, the controller 110 is connected or networked to othersystems or components in the gantry crane 12. The control system canthen monitor and/or control various parameters of the gantry crane 12relevant to the steering modes. These may include engine speed, engineload, machine speed, oil pressure, coolant temperature, fuel level,hydrostatic transmission pressure, wheel position, etc. The controlsystem 10 automatically adjusts such parameters as necessary toimplement the current steering mode or a newly selected steering mode.Additionally, the control system 10 also provides an alert or otherwisewarns of problems with the engine or other devices being monitored. Thepreferred IQAN system can communicate with any other device thatutilizes SAE J1939 or CAN Open communication protocols, over a networkconnection.

Similarly, the control system utilizes the sensed parameters to providediagnostic capabilities that allow the operator to monitor machineoperation or troubleshoot problems. The control system can measure anddisplay values for inputs, outputs, calculated values, electronic engineparameters, hydraulic valve control parameters, or other parametersrelevant to the operation of the crane 12.

One problem with existing systems is that the hydraulic motors that turnthe wheels may not be able to keep up with the requests of the controlsystem in low engine RPM situations. The gantry crane 12 has differentengine modes of operation wherein the engine may be operating at a lowRPM or higher RPMs. The engine RPMs affect how much hydraulic fluid maybe delivered to the hydraulic motors 102. As a result, in a low engineRPM mode, one or more of the wheels might not be in the correct positionfor the steering mode selected. To overcome this result, the controller110 receives input 148 (see FIG. 10) to monitor the current engine RPMs.When the RPMs are high enough to execute the current or selectedsteering mode, the steering system acts normally. However, if the RPMsare too low to execute the current or selected mode, a slower command isexecuted. This turns the relevant wheels at a slower rate.

As discussed above, another problem with existing gantry cranes occurswhen the crane is switched into the carousel mode. In the past, thisrequired positional rotation of two of the wheels approximately 90degrees or more further than the other two wheels, in order for all fourwheels to be in the proper position (to get all wheels driving—i.e.,rotating along the axle of the wheel—in the proper direction). Forexample, if each of the wheels is set to drive forward in a “straightahead” mode, then when switching to a “carousel” mode the right frontwheel 32 can be rotated inwardly (counterclockwise) about 44 degrees andthe right rear wheel 30 can be rotated outward (clockwise) −44 degreesto be in the proper position for the carousel mode; however, because thewheels are set to drive in a forward direction, the left front wheel 36would need to be rotated about 134 degrees (counterclockwise) and theleft rear wheel 34 would need to be rotated about −134 (clockwise, or224 counterclockwise) to position each of the wheels at the appropriateangle with respect to the forward direction to implement the carouselmode in a counterclockwise direction about the center point 105. Thesteering system 10 of the present invention overcomes this problem bycausing the driving direction of rotation of the two problem wheels(about each wheel's axle) to be reversed. This is accomplished byreversing the hydraulic motor associated with these wheels, either via avalve in the motor or by reversing the direction of the electricalcurrent supplied to the motor. As a result, the problem wheels will onlyneed to be rotated approximately 44 degrees (i.e., the left front wheelcan be rotated −44 degrees inward (clockwise) and the rear left wheel 34can be rotated 44 degrees outward (counterclockwise), similar to theother two wheels) to be in the proper position. The carousel modereverse drive solenoid valve control 146, controlled by the controller110 can be utilized for this feature.

The controller 110 can be configured to receive information relating tothe wheel base and width of the gantry crane 12. Moreover, if the widthis changed (e.g., for an embodiment having an adjustable cross-beam 28),the controller 110 can be programmed to automatically adjust therotational position of the various wheels to take the dimensions of thecrane into consideration. For example, the rotational position of thewheels in the carousel mode will depend on the width of the crane andcan vary from the angles described above.

While the specific embodiments have been illustrated and described,numerous modifications come to mind without significantly departing fromthe spirit of the invention, and the scope of protection is only limitedby the scope of the accompanying Claims.

1. A steering system for a crane comprising: a first front wheel and asecond opposing front wheel connected proximate a front portion of thecrane; a first rear wheel and a second opposing rear wheel connectedproximate a rear portion of the crane; and, a control system connectedto the crane having a command potentiometer, a user interfaceelectronically coupled to the command potentiometer, and a programmablecontroller responsive to the command potentiometer for controlling theangular position of each of the first front wheel, the second frontwheel, the first rear wheel and the second rear wheel to effect asteering mode selected through the user interface.
 2. The steeringsystem of claim 1 further comprising: an engine connected to the crane,the engine capable of operation at a variety of different RPMs; and, asensor coupled to the engine and the controller for providing thecontroller with an operating RPM of the engine, wherein if the operatingRPM is lower than a predetermined amount, the controller adjusts therate of change of the angular position of each wheel.
 3. The system ofclaim 1 further comprising: a first sensor for monitoring the angularposition of the first front wheel; a second sensor for monitoring theangular position of the second front wheel; a third sensor formonitoring the angular position of the first rear wheel; and, a fourthsensor for monitoring the angular position of the second rear wheel; thefirst, second, third and fourth sensors coupled to the controllerwherein the controller monitors the angular positions of the wheels andwhen one of the wheels exceeds a predetermined distance between itssensed position and programmed position, the controller stops angularmovement of the remaining wheels.
 4. The steering system of claim 1wherein the controller is programmed to slow down movement of the cranebefore effecting a carousel steering mode selected through the userinterface.
 5. The steering system of claim 1 wherein the controller isprogrammed to move the angular position of each wheel one of clockwiseand counter clockwise, to effect the smallest amount of angular movementnecessary to position each wheel for the carousel steering mode.
 6. Thesteering system of claim 1 wherein the user interface comprises aproportional device that provides a direction and a magnitude signal. 7.The steering system of claim 6 wherein the proportional device comprisesa joystick.
 8. A steering system for controlling the steering mode of acrane comprising: a crane structure having a first front wheel proximatea front portion of a first side of the crane structure, a second frontwheel proximate a front portion of a second side of the crane structure,a first rear wheel proximate a rear portion of the first side, and asecond rear wheel proximate a rear portion on the second side; a userinterface for selecting a steering mode; and, a controllercommunicatively coupled to the user interface, the controller configuredto monitor the position of the first and second front wheels and thefirst and second rear wheels, and to control movement of the first andsecond front wheels and the first and second rear wheels in response toa selected steering mode, the controller further configured to monitoran operating parameter of the crane.
 9. The steering system of claim 8wherein the controller is programmed to disable an engine drive of thecrane prior to positioning the wheels in a selected steering mode, andto enable the engine drive after the wheels are in position to effectthe selected steering mode.
 10. The steering system of claim 9 whereinthe selected steering mode is a carousel steering mode.
 11. The steeringsystem of claim 8 wherein the controller senses the position of eachwheel when implementing the selected steering mode and disables movementof all wheels upon a determination that at least one wheel is not movingto a desired position at a desired rate.
 12. The steering system ofclaim 8 wherein the user interface is mounted to the crane andcommunicatively coupled to the controller via a wire.
 13. The steeringsystem of claim 8 wherein the user interface is mounted to a radiotransmitter and is communicatively coupled to the controller via radiofrequency transmissions.
 14. The steering system of claim 8 wherein theuser interface is a joystick.
 15. The steering system of claim 8 furthercomprising a command potentiometer coupled to the user interface and thecontroller.
 16. The steering system of claim 8 wherein the controller isconfigured to monitor the drive engine RPM rate, and wherein thecontroller lowers a rate of turning each wheel to a desired position forthe selected steering mode upon sensing a low RPM rate.
 17. The steeringsystem of claim 8 wherein the controller is configured to cause thefirst front wheel and the second rear wheel to rotate counterclockwiseto move into position for a selected carousel steering mode, and tocause the second front wheel and the first rear wheel to rotateclockwise to move into position for the carousel steering mode.
 18. Thesteering system of claim 17 wherein the controller is configured toreverse the drive direction of the second front wheel and the secondrear wheel.
 19. A steering system for controlling the steering mode of aboat lifting apparatus comprising: a frame structure having a firstfront wheel proximate a front portion of a first side of the framestructure, a second front wheel proximate a front portion of a secondside of the frame structure, a first rear wheel proximate a rear portionof the first side, and a second rear wheel proximate a rear portion onthe second side; a user interface capable of placing the apparatus in acarousel steering mode; and, a controller communicatively coupled to theuser interface, the controller configured to control movement of thefirst and second front wheels and the first and second rear wheels inresponse to placing the apparatus in the carousel steering mode, andwherein the controller is configured to turn each of the first frontwheel, second front wheel, first rear wheel and second rear wheel one ofclockwise and counterclockwise in a manner to minimize the amount ofturning required by each respective wheel.
 20. A steering system forcontrolling the steering mode of a boat lifting apparatus comprising: aframe structure having a first front wheel proximate a front portion ofa first side of the frame structure, a second front wheel proximate afront portion of a second side of the frame structure, a first rearwheel proximate a rear portion of the first side, and a second rearwheel proximate a rear portion on the second side; a user interface forselecting a steering mode; and, a controller communicatively coupled tothe user interface, the controller configured to control movement of thefirst and second front wheels and the first and second rear wheels inresponse to a selected steering mode, where in response to selection ofa carousel steering mode, the controller is configured to move the firstfront wheel and the second rear wheel in a counterclockwise directionand to move the second front wheel and the first rear wheel in theclockwise direction to place each wheel in the programmed position forthe carousel steering mode.